JP2000031068A - SUBSTRATE FOR GaN CRYSTAL GROWTH - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for GaN crystal growth, wherein a mask layer and a GaN crystal layer around it can be facilitated in being distinguished from each other, the mask layer being a good reference for various processing after the growth of the GaN crystal layer. SOLUTION: Between a base substrate 1 and a mask layer 2, a non- transmission layer 3 is formed in conformity with a pattern of the mask layer which a light of a wave length between an ultraviolet region and an infrared region will be not allowed to pass through the non-transmission layer 3. The non-transmission layer 3 is made of a material which can withstand the crystal growth conditions for a GaN semiconductor. It will not lose the properties of not allowing the transmission of the light, even if exposed to the crystal growth conditions for a GaN semiconductor. As the non-transmission layer, a Bragg reflection layer or an evaporation layer of high melting point metal is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention belongs to the technical field of a substrate for growing a GaN-based semiconductor crystal.

[0002]

2. Description of the Related Art In order to form various semiconductor devices using a GaN-based material, first, a GaN-based crystal is grown on a base substrate (a base crystal substrate). The material of the base substrate can withstand the severe growth conditions of the GaN-based crystal and
It must have good lattice matching with the N-based crystal. However, since such a material is difficult to obtain, sapphire or the like is used as a material for the base substrate, with some knowledge of lattice mismatch.

Conventionally, a method of using such a base substrate to grow a GaN-based crystal through a buffer layer or the like has been generally used.
Dislocations due to lattice mismatch and the like existed at high density. Dislocations are generated at the interface between the base substrate and the GaN-based crystal, and are inherited upward even when the crystal grows and the thickness of the crystal layer increases, forming a continuous defect portion called a dislocation line (threading dislocation). Since the transition impairs the characteristics of the semiconductor device, a method for growing a low-dislocation GaN-based crystal has been required.

[0004] On the other hand, there has been reported a method of obtaining a low dislocation GaN-based crystal using a mask pattern. In this method, first, as shown in FIG.
On the mask 0, a mask layer 20 made of a material (such as SiO ₂ ) on which a GaN-based crystal cannot grow is formed by drawing a specific pattern. Then, a GaN-based crystal is grown starting from a region (non-mask region) 10a where the mask layer 20 is not formed on the base substrate. If the crystal growth is continued even after the crystal has grown to the height of the mask layer 20, the GaN-based crystal grows not only in the thickness direction but also in the lateral direction along the upper surface of the mask layer 20, as shown in FIG. As shown in b), the GaN-based crystal layer 30 embedded and covering the mask layer 20
Becomes

[0005] At this time, in the GaN-based crystal layer 30, a low dislocation portion with little propagation of dislocation lines is formed in a specific portion such as the portion 30a above the mask layer. Where this low dislocation portion is formed depends on the growth conditions, but is formed at a certain position with respect to the mask layer. In other words, if the growth conditions are clear, the position of the low dislocation portion in the GaN-based crystal layer can be roughly known based on the mask layer.

[0006]

However, as described above, the mask layer is made of SiO ₂ on which GaN-based crystals cannot grow.
And a specific material such as SiN _x and is transparent to light in a wide wavelength range including the visible range. Moreover,
The mask layer is formed to be extremely thin, and is difficult to identify because the GaN-based crystal layer is buried inside when grown.

Therefore, in determining the position of a low dislocation portion in the GaN-based crystal layer and the position of the mask layer itself, the mask layer itself is not used as a reference, for example, with reference to the outer end surface of the base substrate. For example, a method other than a mask layer is used as a reference, such as a method or a method of forming a reference pattern on the back surface of a base substrate.

The present inventors have found that in the method of growing a GaN-based semiconductor crystal using a mask layer, it is difficult to identify the mask layer. It was raised as a problem that it was not obtained and was not paid attention. An object of the present invention is to facilitate the discrimination between a mask layer and a surrounding GaN-based crystal layer,
An object of the present invention is to provide a GaN-based crystal growth substrate having a mask layer that can serve as a preferable reference for various processes after growing the base crystal layer.

[0009]

The GaN-based crystal growth substrate of the present invention has the following features. (1) A mask layer is provided on a base substrate surface on which a GaN-based crystal can be grown so as to form a mask region and a non-mask region, and the mask layer is substantially G from its own surface.
The mask layer and the base substrate are made of a material that cannot grow an aN-based crystal, and an impermeable layer that does not transmit light having a wavelength selected from ultraviolet light to infrared light is formed between the mask layer and the base substrate. The opaque layer is made of Ga
It is made of a material that can withstand the conditions for crystal growth of an N-based semiconductor,
A substrate for growing a GaN-based crystal, wherein the substrate does not lose the property of not transmitting the light even when exposed to crystal growth conditions of the GaN-based semiconductor.

(2) The substrate for growing a GaN-based crystal according to (1), wherein the opaque layer comprises a Bragg reflection layer.

(3) The substrate for growing a GaN-based crystal according to the above (1), wherein the opaque layer is a layer made of a material that does not transmit light having a wavelength in a part or all of the visible region.

(4) The substrate for growing a GaN-based crystal according to (1), wherein the mask layer is formed as a stripe pattern in which strip-shaped mask regions and non-mask regions are alternately arranged.

In this specification, if the lattice plane of a hexagonal lattice crystal such as a GaN-based crystal or a sapphire substrate is specified by four Miller indices (hkil), for convenience of description, when the index is negative, the index is negative. Is indicated with a minus sign in front of, and the notation method for the negative exponent is the same as that of the general Miller index. Therefore, in the case of a GaN-based crystal, there are six prism surfaces (singular surfaces) parallel to the C axis. For example, one of the surfaces is expressed as (1-100), and the six surfaces are grouped as equivalent surfaces. In this case, it is described as {1-100}. Also, planes perpendicular to the {1-100} plane and parallel to the C-axis are equivalently collectively denoted as {11-20}. Also, (1-1)
The direction perpendicular to the (00) plane is [1-100], and the set of directions equivalent thereto is <1-100>. The direction perpendicular to the (11-20) plane is [11-20]. The set is described as <11-20>. However, if there is a case where the Miller index is written in the drawing, when the index is negative, a minus sign is added above the index, and all of the general Miller index notation methods are followed. The crystal orientations referred to in the present invention are all orientations based on a GaN-based crystal grown on a base substrate.

The "mask region" (ie, the masked region) and the "unmasked region" (ie, the unmasked region) are both regions in the base substrate plane. The region on the upper surface of the mask layer is regarded as being equal to the mask region, and is used in the description as synonymous.

[0015]

[Function] The phrase "does not transmit light having a wavelength selected from ultraviolet light to infrared light" means that the layer has an intended specific wavelength of light of a part or all wavelengths in the ultraviolet to infrared range. the light,
It has the property of absorbing and / or reflecting. Among these, the light absorption is the absorption of the substance itself due to the size of the band gap. By absorption, there may be emission of light, such as luminescence light. In addition, the reflection of light is reflection of light due to the property of an opaque material such as a metal, or reflection due to a structure designed and configured to reflect light of a specific wavelength such as a Bragg reflection layer. Further, "not transmit light" means not only completely not transmitting light but also any light that does not transmit light in a range where the object of the present invention is achieved. In other words, the absorptance / reflectance in light absorption / reflection may be any value as long as the impermeable layer can be easily visually or optically identified.

Above all, the wavelength range in the visible range and its vicinity (3
By preventing light having a wavelength of about 50 nm to 800 nm from being transmitted, identification becomes easy. Further, the range of the non-transmissive wavelength range may be limited to the visible range, and a mode in which a person can identify only by visual observation may be adopted.

By forming an opaque layer between the mask layer and the base substrate, the position of the mask layer is identified by the underlying opaque layer. There is no problem even if it is regarded as the position of the mask layer.

The substrate for growing a GaN-based crystal is placed under a high temperature of 1000 ° C., which is a condition for growing a GaN-based crystal. Therefore, the impermeable layer does not melt or decompose even when exposed to the conditions for crystal growth of the GaN-based semiconductor, and has mechanical properties within a range usable as a GaN-based crystal base material.
It is necessary to use a material that can survive as a layer. At the same time, it is important that the property of not transmitting the light is not lost even when exposed to the conditions for crystal growth of the GaN-based semiconductor. "Not lost" here is not just the same. The wavelength of reflection / absorption and the degree of reflection / absorption may be changed by high temperature or the like, and it is sufficient that the opaque layer has properties that can be visually or identifiable by optical measurement.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a substrate for growing a GaN-based crystal according to the present invention has a mask layer 2 formed on a substrate surface of a base substrate 1 such that a mask region d and a non-mask region e are formed. An impermeable layer 3 is provided between the mask layer 2 and the base substrate 1, that is, below the mask layer.
Are formed in conformity with the formation pattern of.

The base substrate may be any substrate as long as the GaN-based crystal can grow with the C axis as the thickness direction. For example, sapphire, quartz, SiC, or the like, which has been widely used for growing a GaN-based crystal, may be used. Above all,
A sapphire C-plane, A-plane, or 6H-SiC substrate, particularly a C-plane sapphire substrate is preferred. In addition, these substrates are used as basic crystal substrates, and ZnO, Mg for reducing the difference in lattice constant and thermal expansion coefficient from GaN-based crystals is provided on the surface.
A substrate provided with a buffer layer such as O or AlN may be used as the base substrate.

It is desirable that the base substrate has a lattice constant and a thermal expansion coefficient as close as possible to the GaN-based crystal to be grown, so that defects such as dislocations are reduced, and cracks and the like are more unlikely to occur. . Also,
It is desirable that the mask layer has excellent resistance to high heat and etching when forming the mask layer. From this point of view, at least the surface layer of the base substrate _{In X Ga Y Al Z N (} 0 ≦ X
≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1). For example, as shown in FIG. 1, the surface of the crystal substrate 1a of the foundation, such as sapphire, via the buffer layer 1b, and In _X Ga _Y Al _Z N layer 1c is grown as a surface layer, which as the base substrate 1 This is the mode of use. Specifically, a layer in which a buffer layer of ZnO, AlN, or the like and then a thin layer of GaN or GaAlN are sequentially formed on a sapphire substrate by MOVPE can be preferably used. With such a base substrate, the density of dislocations newly generated in the GaN-based crystal grown on the base substrate can be kept low, and good crystallinity can be obtained.

The opaque layer may be present as a layer between the mask layer and the base substrate. However, since the purpose is to make the mask layer identifiable, it is directly adjacent to the mask layer as a lower layer of the mask layer. It is desirable to do. Hereinafter, a configuration including only the base substrate, the opaque layer, and the mask layer will be described.

FIG. 2 shows a specific embodiment of the impermeable layer.
As shown in (a), a layer 3a made of an opaque material such as a metal layer, or as shown in FIG. 2 (b), a reflective layer having a multilayer structure designed and configured to be reflective such as a Bragg reflective layer. 3b, which can withstand the conditions for crystal growth of a GaN-based semiconductor.

As the material of the layer 3a made of an opaque material as shown in FIG. 2 (a), particularly the material of the metal layer, there are high melting point materials such as W and Ti. The reflection layer 3b as shown in FIG.
As a structure that can withstand the growth conditions of the aN-based crystal, AlGa
A multilayer film including a combination of GaN-based crystal layers, such as a combination of N / GaN, may be used. In particular, it is preferable to form a pair of two GaN-based crystal layers constituting a superlattice and to stack a desired number of the pairs because of high reflectance.

The mask layer is made of a material that does not allow a GaN-based crystal to grow substantially from its own surface. As such a material, for example, an amorphous body is exemplified, and Si
O ₂ and SiNx are exemplified. In particular, SiO ₂ is excellent in heat resistance and relatively easy to form and remove by etching.
A membrane can be suitably used.

The formation pattern of the mask layer is important because it has a great influence on how the GaN-based crystal grows and how dislocation lines propagate. In particular, the ratio between the mask region and the non-mask region and the direction of the boundary line between the mask region and the non-mask region are important. The direction of this boundary line will be described.

(A) When the boundary between the mask region and the non-mask region is a straight line in the <1-100> direction, Ga that grows in the lateral direction along the upper surface of the mask layer beyond this boundary.
The plane of the N-based crystal is a {11-20} plane. ｛11-2
Face 0 is off-facet, so facet {1}
The GaN-based crystal grows faster in the lateral direction than the -100 ° plane. When the lateral growth rate increases, ｛1-10
It is difficult to form an oblique facet such as a 1｝ plane. As a result, when the mask layer is buried flat, the thickness of the GaN-based crystal layer can be smaller than in the case of (b) below.

(B) When the boundary between the mask area and the non-mask area is a straight line in the <11-20> direction, the facet {1-100} plane grows laterally beyond this boundary. And the growth rate in the lateral direction is reduced. Since the growth rate in the C-axis direction is faster than the lateral growth rate,
Oblique facets such as the 101 ° plane are easily formed. As a result, the GaN-based crystal layer needs to have a certain thickness to bury the mask layer flat.

An example of a formation pattern useful for forming a GaN-based semiconductor device is a stripe pattern. The stripe pattern is a pattern in which strip-shaped mask layers are arranged in stripes. Therefore, the band-shaped mask regions and the band-shaped non-mask regions are alternately arranged. The longitudinal direction of this band is the direction of the boundary between the mask region and the non-mask region.

An example of a method for forming the mask layer and the impermeable layer is as follows. (A) covering the entire surface of the base substrate with a layer serving as an impermeable layer,
(B) further covering the entire surface with a layer serving as a mask layer,
(C) Thereafter, the photosensitive resist is patterned by a photolithography technique, and both the mask layer and the impermeable layer are removed by etching to expose a non-mask region of the base substrate.

In the above (a), when the impermeable layer is a metal layer, the impermeable layer is preferably formed by a vacuum evaporation method, a sputtering method, or the like. When the opaque layer is a Bragg reflection layer, a crystal growth method such as MOVPE is preferable. The formation of the mask layer in (b) above is preferably performed by a method such as vacuum deposition, sputtering, or CVD. The total thickness of the mask layer and the opaque layer together is
Usually, about 50 nm to 500 nm is a preferable value.

The wavelength of light to be reflected by the Bragg reflection layer is not limited.
The extent of the degree is easy for optical identification. In addition, as described in the above description of the operation, if the design and use of the Bragg reflection layer is designed to reflect light in the visible range, it becomes convenient because the identification can be made with the naked eye. Although any material can be used for the Bragg reflection layer, a material that can withstand the growth conditions of the GaN-based crystal is preferable. For example, a GaN / AlGaN multilayer film can be used.

Since the mask layer is visually or optically identifiable by the opaque layer, for example, the type of the mask layer formation pattern and the management number are placed in a useless area near the outer peripheral edge on the base substrate surface. Can be displayed using a mask layer / impermeable layer. In other words, when patterning the mask layer / impermeable layer, if necessary display contents are drawn by a resist film, no special cost is required,
An image is displayed by the mask layer / impermeable layer. This facilitates handling and management of the substrate not only after the crystal growth but also before the crystal growth.

Using the substrate for growing a GaN-based crystal according to the present invention, the GaN-based crystal is grown until the mask layer is covered using the unmasked region on the substrate as a starting surface for crystal growth, for example, as in FIG. By growing the layer, G
A GaN-based crystal base material that can visually or optically identify the position of the mask layer embedded in the aN-based crystal layer is obtained.

The GaN-based crystal to be grown using the GaN-based crystal growth substrate according to the present invention is represented by the formula In _x Ga _Y.
Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X +
Y + Z = 1). In particular,
Useful as thick film layers are GaN, AlGaN,
InGaN is a typical example.

[0036]

EXAMPLE Hereinafter, a substrate for growing a GaN-based crystal according to the present invention was actually manufactured, and a GaN-based crystal was grown on the substrate to confirm the discriminability of the mask layer. Example 1 This example is an example in which the impermeable layer is a metal layer (tungsten layer). [Preparation of base substrate] As shown in FIG.
The most basic crystal substrate 1a has a diameter of 2 inches and a thickness of 3 inches.
A 30 μm sapphire C-plane substrate was used. First, this sapphire substrate was placed in an MOCVD apparatus, heated to 1100 ° C. in a hydrogen atmosphere, and subjected to thermal etching. Thereafter, the temperature was lowered to 500 ° C., and trimethylaluminum (hereinafter referred to as TMA) as an Al material and ammonia as an N material were flown to grow the AlN low-temperature buffer layer 1b. Subsequently, the temperature was raised to 1000 ° C., and trimethylgallium (hereinafter, TMG) was flowed as a Ga raw material, and ammonia was flown as an N raw material.

[Formation of Mask Layer] A tungsten layer is formed by vapor deposition, and a tungsten layer having a thickness of 10
A 0 nm SiO ₂ layer was formed. Thereafter, the photosensitive resist was patterned by photolithography, and a striped mask layer composed of a SiO ₂ layer / tungsten layer was formed by etching. The longitudinal direction of the stripe band is <11-
20> direction to obtain a substrate for growing a GaN-based crystal according to the present invention.

[Growth of GaN Crystal] Next, this sample was
Hydrogen atmosphere (including ammonia) placed in CVD equipment
Then, the temperature was raised to 1000 ° C. to remove TMG and ammonia for 30 minutes.
GaN crystal was grown to cover the upper surface of the mask layer to form a GaN crystal base material. The GaN crystal is first grown to have a pyramid shape in the non-mask region,
It became flat with a thickness of about 10 μm from the base substrate surface.

The position of the mask layer embedded in the GaN crystal layer of the obtained GaN crystal base material can be clearly grasped, and is a preferable positioning standard for processing a low dislocation portion in the GaN crystal layer. It was gaining.

Embodiment 2 This embodiment is an example in which the opaque layer is a Bragg reflection layer. [Formation of Bragg Reflection Layer and SiO ₂ Layer] On the same base substrate 1 as in Example 1, a Bragg reflection layer having a reflection peak wavelength of 450 nm was formed by MOCVD to form a GaN / A
As a multilayer film of l _0.1 Ga _0.9 N 4 pairs, the multilayer film was laminated so as to cover the entire upper surface of the base substrate. The total thickness of the Bragg reflection layer was 366 nm. Further, a 100-nm-thick SiO ₂ layer covering the entire upper surface of the Bragg reflection layer was formed by a sputtering apparatus.

[Patterning of Mask Layer] The photosensitive resist is patterned by photolithography.
A striped mask layer composed of a SiO ₂ layer / Bragg reflection layer was formed by etching. The longitudinal direction of the stripe band is <11-2 of the growing GaN-based crystal.
0> direction to obtain a GaN-based crystal growth substrate according to the present invention.

[Growth of GaN Crystal] Next, this sample was
Placed in a CVD apparatus, and under the same conditions as in Example 1, Ga
An N crystal was grown until it covered the mask layer to obtain a GaN crystal base material. The GaN crystal was first grown to have a pyramid shape in the non-mask region, and then flattened to a thickness of about 10 μm from the base substrate surface.

The obtained mask layer of the GaN crystal base material is light purple to the naked eye. In particular, the position of the mask layer can be clearly confirmed by irradiating light of 400 nm and observing with a photographing device. Was.

[Formation of Second Mask Layer] On the surface of the GaN crystal layer, based on the inside colored mask layer,
A second mask layer was further formed in a stripe shape at a position corresponding to above the non-mask region. The workability of the second mask layer, which was performed with reference to the lower mask layer, was good.

[Growth of GaN Crystal Layer of Second Layer] This sample was placed in an MOCVD apparatus, and a GaN crystal layer was grown until the second mask layer was buried in the same manner as described above.
As a result, dislocation lines generated from the interface between the substrate and the buffer layer and extending to the upper layer side are sufficiently blocked by the two (two-stage) mask layers, and the second GaN crystal layer is sufficiently A low dislocation GaN layer was obtained.

[0046]

The substrate for growing a GaN-based crystal of the present invention has a G
Regardless of before and after the growth of the aN-based crystal layer, the mask layer can always be easily visually and optically identified by the impermeable layer. Therefore, the mask layer itself can always be focused on, and in particular, G
After the growth of the aN-based crystal layer, it can serve as a preferable standard for determining the position of a low dislocation portion in the crystal layer and forming an upper mask layer, which is preferable for management and processing.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a GaN-based crystal growth substrate of the present invention.

FIG. 2 is an enlarged cross-sectional view of one of a mask layer and an opaque layer in a GaN-based crystal growth substrate of the present invention. FIG.
(B) expresses that it is multilayer by four layers.

FIG. 3 is a diagram showing a conventional method for growing a GaN-based crystal using a mask layer, and FIG. 3B is a cross-sectional view. The hatching indicating the cross section is omitted.

[Explanation of symbols]

 Reference Signs List 1 base substrate 2 mask layer 3 non-transmissive layer d mask area e non-mask area

Continued on the front page (72) Inventor Kazuyuki Tadomo 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Itami Works F-term (reference) 5F041 AA40 CA40 CA67 CA77 5F045 AA04 AB09 AB14 AB17 AB18 AC08 AC12 AD09 AD14 AF02 AF09 AF13 AF20 BB12 EB15

Claims (4)

[Claims] A mask layer is provided on a base substrate surface on which a GaN-based crystal can be grown so as to form a mask region and a non-mask region, and the mask layer is substantially GaN-based from its own surface. The mask layer is made of a material that cannot grow, and an opaque layer that does not transmit light having a wavelength selected from ultraviolet light to infrared light is provided between the mask layer and the base substrate. The opaque layer is made of a material that can withstand the conditions for crystal growth of the GaN-based semiconductor, and loses the property of not transmitting the light even when exposed to the conditions for crystal growth of the GaN-based semiconductor. A substrate for growing a GaN-based crystal, which is not provided. 2. The GaN-based crystal growth substrate according to claim 1, wherein the opaque layer comprises a Bragg reflection layer. 3. The GaN-based crystal growth substrate according to claim 1, wherein the opaque layer is a layer made of a material that does not transmit light having a wavelength in a part or all of the visible region. 4. The GaN-based crystal growth substrate according to claim 1, wherein the mask layer is formed as a stripe pattern in which strip-shaped mask regions and non-mask regions are alternately arranged.